An increase in environmental concerns has continued to drive strict regulations of the hydrocarbon emissions from automotives into the environment, even when the vehicle is not operating. The great majority of internal combustion engines in use today are fuel-injected engines. When a fuel-injected engine is switched off after use, a small amount of residual fuel volatilizes and escapes from the injector tips. While a vehicle is sitting over time after use, this evaporated fuel may pass outwardly through the intake manifold, the intake air ducts and air filter, and may escape into the atmosphere, thus contributing to air pollution. Therefore, it would be desirable to minimize this type of inadvertent evaporative emissions leakage.
Several approaches have been used to control the hydrocarbon vapors escaped from the intake manifold after engine shutdown.
An engine's electronic throttle control may be used to close the intake manifold at the engine shutdown, and thereby minimizing the hydrocarbon emission to the atmosphere. However, this approach may impair the desirable option of a so-called “limp-home” mode in which a vehicle may be driven in the event of a partial failure of the engine electronics control system. For systems with mechanical throttle control, it is difficult and expensive to completely seal the intake manifold and thereby preventing the escape of hydrocarbon vapors from the manifold to the atmosphere.
U.S. Pat. No. 7,168,417 describes a hydrocarbon trapping device for an engine's air intake system including a conduit pressed fit into the air duct, a carbon adsorbent sheet extending substantially completely around the inner perimeter of the conduit, and a retainer extending from the inner surface of the conduit to retain the side edge of the absorbent sheet. Unfortunately, the approach is only partially successful because the hydrocarbon vapor laden air can escape the manifold without being brought into proximity with a carbon adsorptive surface. As a result, relatively large areas of carbon sheeting are required to ensure that an adequate quantity of the laden air comes into contact with the carbon adsorptive surface.
U.S. Pat. No. 6,692,551 discloses an air intake emission control system for controlling the hydrocarbon emission having a rigid carbon monolith adsorbent disposed in a conduit connecting between an air box and an atmospheric air intake port. The carbon monolith is, however, brittle and vulnerable to breakage due to incidental impact during handling and installation. Vibration during engine operation or vehicle travel over non-smooth road surfaces may also result in damage during use. Such damage may dislodge particles that restrict air flow to the engine or are drawn into the intake manifold and potentially adversely affect engine operation. Furthermore, the monolith structure creates a large and undesirable flow restriction (i.e. pressure drop) in the intake air flow path due to a large cross-sectional area of its structure and its relatively small-diameter air passages. It is desirable to have an emission control system for the intake manifold with minimum air flow resistance, since both engine performance and fuel efficiency can be adversely affected by the flow restriction.
U.S. Pat. No. 7,222,612 describes a low-resistance hydrocarbon-adsorptive cartridge for an air intake of an internal combustion engine comprising a structure for being mounted into a portion of an engine air intake system. The structure is adapted to orient and retain one or more thin sheets of activated carbon sheeting in the intake system. The plurality of sheets is oriented such that the leading edge of each sheet is presented to the engine intake air stream, thereby minimizing reduction in total cross-sectional area of the intake system.
Several AIS emission control devices currently used in an automotive industry rely on passing the contaminant-laden air through a carbon adsorbent element with particular limited design. The contaminant-laden air flows through the carbon adsorbent element located in the air box, and the hydrocarbon vapors are adsorbed onto the carbon adsorbent. Unfortunately, these flow-through air intake emission control devices have high flow restriction (i.e., pressure drop) in the intake air flow path, and both engine performance and fuel efficiency can be adversely affected by the high flow restriction. Furthermore, these devices have limited adsorption efficiency for the hydrocarbon vapors.
Accordingly, there is a need for an AIS emission control device capable of reducing the leak of hydrocarbon vapors from the engine's intake manifold into the atmosphere during engine shutdown that has enhanced hydrocarbon adsorption capacity and efficiency; minimum air flow resistance with the device present in the air induction system; and sufficient strength to sustain the structural integrity during installation and operation of the vehicle.